The present invention relates to a scanning line position control system, and more particularly to a scanning line position control system for controlling the position of scanning lines on a CRT video monitor to produce images of as good quality as possible when such images displayed on the CRT video monitor are photographed to produce hard copies on photographic films.
For the preservation of a image displayed on a CRT video monitor, it has been practiced to photograph such a displayed image with a camera to produce a hard copy on a photographic film. Since no image is actually displayed between scanning lines on the CRT video monitor, the photographed image on the film suffers a high contrast between the scanning lines and spaces between the scanning lines, with the result that no hard copies of good quality can be produced.
Various attempts have heretofore been made to solve the aforesaid problem. One effort has been to add a small oscillating signal to a vertical synchronizing signal for a CRT video monitor. This method has been disadvantageous because it requires a high level of technique in order to add a high-frequency oscillating signal, which is small enough not to damage image information to be recorded, to the vertical synchronizing signal. According to another process, a vertical synchronizing signal is successively delayed by a monostable multivibrator. The desired delay time is set by a time-constant circuit composed of a capacitor and a resistor. However, the delay time may not be stable at all times due for example of temperature variations. Furthermore, where image signals are displayed by the interlaced scanning system, scanning lines cannot be erased if scanning lines in an even field are not accurately positioned between scanning lines in an odd field.